Parts conveyor pallet and means for supporting same on an initial pair of rails and switching same to a second pair of rails

ABSTRACT

A pallet for conveying parts through a succession of work stations. The primary support for the pallet comprises a pair of vertically aligned tubular rails. The pallet is supported on these rails by a pair of upper rollers mounted on said pallet and riding on the upper rail and a pair of lower rollers mounted on said pallet and riding on the lower rail along with a third pair of intermediate or clamping rollers, shiftably mounted on said pallet, which cooperates with the upper rollers to clamp the pallet to the upper rail. In this manner the pallet is cantilevered from the top rail. The first mentioned rails are disposed in a continuous path. Each work station is mounted to one side of said path. For each work station there is a side pair of vertically aligned rails extending closely adjacent to and parallel to said first mentioned rails a relatively short distance, then leaving said first mentioned rails to lead to a said work station, and then extending back to said first mentioned rails wherein said side pair of rails is again closely adjacent to and parallel to said first mentioned rails a relatively short distance. Said pallet has mounted thereon a second pair of upper rollers, and a second pair of lower rollers, disposed to engage said side pair of rails when the pallet is brought to that position wherein the side pair of rails is parallel to said first mentioned rails. At this last mentioned point means are actuated to disengage said third pair of rollers from clamping engagement with said first mentioned upper rail while immediately causing a similar pair of clamping rollers to engage the upper of said side pair of rails whereby said pallet is then cantilevered from said side pair of rails by virtue of said second pair of upper rollers, said similar pair of clamping rollers and said second pair of lower rollers.

United States Patent 1 Lott et al.

{451 Feb. 20, 1973 [75] Inventors: George T. Lott, Wyoming; Francis H.Little, Cincinnati, both of Ohio [73] Assignee: Lott Tool Corporation,Cincinnati,

Ohio

[22] Filed: May 3, 1971 [21] Appl. No.: 139,672

[52] US. Cl ..104/l30, 105/141 [51] Int. Cl. ..E01b 25/26 [58] FieldofSearch ..l04/l30, 132', 118, 119, 121,

[56] References Cited UNITED STATES PATENTS 3,099,966 8/ 1963 Bishop etal ..l04/96 3,628,462 12/ 1971 Holt ..l04/130 Primary Examiner-Robert J.Spar Attorney-Melville, Strasser, Foster & Hoffman [57] ABSTRACT Apallet for conveying parts through a succession of work stations. Theprimary support for the pallet comprises a pair of vertically alignedtubular rails. The pallet is supported on these rails by a pair of upperrollers mounted on said pallet and riding on the upper rail and a pairof lower rollers mounted on said pallet and riding on the lower railalong with a third pair of intermediate or clamping rollers, shiftablymounted on said pallet, which cooperates with the upper rollers to clampthe pallet to the upper rail. In this manner the pallet is cantileveredfrom the top rail. The first mentioned rails are disposed in acontinuous path. Each work station is mounted to one side of said path.For each work station there is a side pair of vertically aligned railsextending closely adjacent to and parallel to said first mentioned railsa relatively short distance, then leaving said first mentioned rails tolead to a said work station, and then extending back to said firstmentioned rails wherein said side pair of rails is again closelyadjacent to and parallel to said first mentioned rails a relativelyshort distance. Said pallet has mounted thereon a second pair of upperrollers, and a second pair of lower rollers, disposed to engage saidside pair of rails when the pallet is brought to that position whereinthe side pair of rails is parallel to said first mentioned rails. Atthis last mentioned point means are'actuated to disengage said thirdpair of roll ers from clamping engagement with said first mentionedupper rail while immediately causing a similar pair of clamping rollersto engage the upper of said side pair of rails whereby said pallet isthen cantilevered from said side pair of rails by virtue of said secondpair of upper rollers, said similar pair of clamping rollers and saidsecond pair of lower rollers.

6 Claims, 7 Drawing Figures PATENTEB FEB20 I973 sum 1 OF 5,

PARTS CONVEYOR PALLET AND MEANS FOR SUPPORTING SAME ON AN.INITIAL PAIROF RAILS AND SWITCHING SAME TO A SECOND PAIR OF RAILS BACKGROUND OF THEINVENTION 1 Field of the Invention This invention has wide application.It is useful in those industries wherein a given part is to have anumber of machining operations performed thereon. The pallet-conveyor ofthis invention enables such a part to be taken substantiallysequentially through a number of work stations disposed to one side of amain track. Although the instant invention is particularly suitable foruse in the automobile industry wherein a number of parts weighing withinthe range of 50 to 150 pounds must undergo successive machiningoperations, it will be obvious to those skilled in the art that thisinvention may have much greater use than that. It will be equallyobvious that with relatively minor adjustments the pallet may be adaptedto convey much lighter or much heavier loads than indicated.

2. Description of the Prior Art No search has been made in the UnitedStates Patent Office to determine whether or not a pallet-conveyorsystem like that comprising the instant invention is shown in any issuedUnited States patent. Although the inventors have a fairly extensivepersonal knowledge of this general art, they are not aware of any partconveying pallet arranged for cantilevered support from one set ofvertically aligned rails and shiftable to similar cantilevered supportfrom a second set of vertically aligned rails while the pallet is drivenby combinations of continuously moving chains and the like.

SUMMARY OF THE INVENTION- Heretofore problems have arisen respecting theefficient handling of parts and the like which must have a plurality ofoperations performed thereon. It is expensive and time consuming totransport such parts, step by separate step, from one place to another.It is not always practicable to station the part in one place and changetools one way or another. Mechanisms which have attempted to routepieces for successive operations in the past have proved complicated,subject to timing difficulties and expensive. The present inventionsolves these and other problems by providing a part conveying palletwhich may be supported, selectively, on various sets of verticallyaligned rails, two each. The pallet is provided with two pairs of upperrollers, one pair at either side thereof, and two pairs of lowerrollers, one pair at either side thereof. Intermediate these upper andlower rollers, which are fixed in position on the pallet, is a pair ofshiftable arms linked together for simultaneous movement. Each arm has aclamping roller at either end thereof. In the normal position the palletis supported on the main track comprised of a pair of vertically alignedrails by virtue of the upper and lower rollers stationed on the sameside of the pallet and riding on the upper and lower rails comprisingsaid main track. The corresponding clamping rollers engage the upperrail whereby the pallet is cantilevered from the main track. When thepallet is moved along the main track until such time as the upper andlower rollers on the side opposite the main track come into contact withthose portions of vertically aligned upper and lower rails comprising aside track, the side track being initially parallel to the main track,the pallet thus being supported simultaneously for a brief period onboth the main track and the side track, the shiftable arms are actuatedduring such brief period whereby to disengage the clamping rollers fromthe main track upper rail and to immediately engage the other clampingrollers with the upper rail of the side track whereby the pallet isthereby cantilevered from the side track. During this brief period thepallet is driven by both the main track drive and the side track drive,each drive following its respective track, by virtue of means on thepallet adapted to engage both drives simultaneously when the tracksparallel one another, at such time the tracks also being closelyadjacent one another.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of thepallet and conveyor mechanism (partially fragmentary) according to thisinvention,

FIG. 2 is a front elevation taken from the right side of FIG. 1,

FIG. 3 is a schematic plan view showing the general arrangement of themain track and a plurality of side tracks and work stations to beserviced by the palletconveyor system of this invention,

FIG. 4 is a front-elevation, with parts broken away, of the pallet andtrack mechanisms included within the scope of this invention showing thepallet clamped in cantilevered condition on the main, left-hand trackmeans as viewed in this Figure,

FIG. 5 is a view similar to FIG. 4 but with the pallet clamped incantilevered condition on the side, righthand track means as viewed inthis Figure,

FIG. 6 is a perspective view of portions of the pallet and trackmechanisms, and

FIG. 7 is a view similar to FIG. 4 but showing the pallet cantileveredon the main track in an area of the system wherein there is no sidetrack.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIGS. 6 and3, the basic elements of the involved mechanisms will be described.The'parts conveyor pallet is generally indicated at 10. This pallet 10is arranged to ride on and along a main track comprised of a pair ofvertically aligned, tubular rails 11a and 11b. From time to time,however, the pallet will ride on and along one or more side tracks eachof which is comprised of a pair of vertically aligned, tubular rails 12aand 12b. journaled in the pallet 10 is a first pair of upper rollers 13and a second pair of upper rollers 14. Also journaled in this pallet 10is a first pair of lower rollers 15 and a second pair of lower rollers16. All of these rollers 13, l4, l5 and 16 are fixed in position on thepallet 10.

Intermediate the pairs of upper and lower rollers is a first pair ofclamping rollers 17 and a second pair of clamping rollers 18. Eachclamping roller 17 is journaled on one end of a separate arm 19a, 19b;the clamping rollers 18 are mounted on the other ends of these arms 19aand 19b. The arms 19a and 19b are fixed on a rod 20 so that they willmove together. The rod 20 is suitably journaled in the pallet 10. In theposition shown in FIGS. 6 and 7 the clamping rollers 17 are engaged withthe upper rail 11a so that, by virtue of the rollers 13, 15 and 17, thepallet is cantilevered from the main track comprised of the verticallyaligned, tubular rails 11a and 111). It is true, however, that duringthe time portions of the side track rails 12a, 12b are parallel to themain track rails 11a, 11b the rollers 14 and 16 will engage therespective rails 12a, 12b; this is the condition specificallyillustrated in FIG. 6. FIG. 7, therefore, shows the pallet 10 assupported from the main track rails 11a, 11b either prior to, or after,the pallet is brought into the vicinity of any of the side tracks 12a,12b.

Fixed on one side of the arm 19a is a back piece or cam plate 21. Thisis perhaps best seen in FIGS. 1 and 2. The cam plate 21 has downwardlyprojecting cam portions 22 and 23 located at the opposite ends thereof.A shift bar 24 is slidably arranged in the pallet 10 between a first anda second position. The bar 24 is partially cut away at 25 and 26 toaccommodate a pair of cam rollers 27 and 28 which are journaled on thebar 24. In view of the fact that the bar 190, the cam plate 21, the rod20 and the bar 19b all move together as a unit when actuated by movementof the bar 24 as will be further described, only one such shiftable bar24 is required.

In the first position of the shiftable bar 24 the roller 27 engages thecam projection 22 whereby to move the cam plate 21 and the arm 19a intosuch position that the. clamping rollers 17 engage the upper rail 1 laof the main conveyor track. This is best seen in FIGS. 2, 4 and 6. Inthis position, as is best seen in FIG. 7, the pallet 10 is cantileveredfrom the main track 11a, 11!; by virtue of engagement of the upperrollers 13 with the upper tubular member 110, engagement of the clampingrollers 17 with this same tubular member 11a, and engagement of thelower rollers with the lower tubular member 11b. The pair of upperrollers 14 and pair of lower rollers 16 are out of engagement withanything at this point as are also the clamping rollers 18. When,however, the pallet 10 comes to a point wherein the side track rails12a, 12b are parallel to the main track rails 11a, 11b the rollers 14and 16 are so positioned that they will contact these side track rails.The clamping rollers 18, however, at the very point the rollers 14 and16 first come into contact with the rails 12a, 12b will be spaced fromthe rail 120 until the shiftable bar 24 is actuated. Thus the mainsupport for the pallet 10 at this point continues to be its cantileveredarrangement with respect to the main track rails 1 14, 11b.

When the pallet 10 is in position with respect to the main track rails"11a, 11b and the side track rails 12a,

I 12b as indicated in FIGS. 4 and 5, this being that stage whereinportions of the rails 11a, 11b, 12a and 12b are parallel to one another,it again being noted that initially the pallet 10 is cantilevered fromthe main track rails 11a, 11b as indicated in FIGS. 4 and 7, and it isdesired to shift the cantilever support from the main track to the sidetrack, the shifiable bar 24 is moved from left to right as viewed inFIG. 4. Such movement of the bar 24 will bring the various operatingparts into the position shown in FIG. 5. Movement of the bar 24 may beaccomplished by any conventional means such as an air operated plungergenerally indicated at 29 in FIG. 4. Movement of the bar 24'from theleft-hand position shown in FIG. 4 to the right-hand position shown inFIG. 5 results in the roller 27 moving away from the depending camsurface 22 of the back cam plate 21 fixed to the arm 190 while the camroller 28 will move into contact with the cam surface 23, also a part ofthe cam plate 21, whereby to rock the plate 21 and arm 19a in acounterclock-wise direction along with the rod 20. This movement of thearm 19a, and also of the similar arm 19b which is fixed on the rod 20 asearlier described, brings the clamping rollers 17 out of contact withthe upper main track rail l la while simultaneously bringing theclamping rollers 18 into clamping engagement with the upper side trackrail 12a whereby the pallet 10 is cantilevered from the side track 12a,12b by virtue of the rollers 14 and 16 in cooperation with the clampingrollers 18. As noted earlier, this shift of the pallet 10 from itscantilevered support from the main track 11a, 11b to its similarcantilevered support from the side track 12a, 12b occurs when portionsof the main track and side track are parallel to one another. Continuedmovement of the pallet 10 in a manner to be described shortly results inthe pallet moving'along the side track 12a, 12b into position before anappropriate work station. This is generally indicated in FIG. 6 and isshown in somewhat greater detail in FIG. 3.

The pallet 10 is driven by means of one or more downwardly extendingarms generallyindicated at 30 in FIGS. 1 and 2; these arms arepreferably spring loaded as shown in these Figures. Fastened to thelower ends of these arms is a plate 31 having some sort of frictionmaterial on the underside thereof. This spring loaded friction plate 31frictionally engages the top of a flat segmented (crescent) chain, whichis well known in the art, and which is disposed beneath the pallet ascantilevered from the main track 11a, 11b. This chain is continuouslydriven at a constant speed by conventional means, not shown, duringoperation of the palletconveyor mechanism. The spring loaded arms 30 andfriction plate 31 cooperate with the rollers 13, 15 and 17 to supportthe pallet 10; the arms 30 and plate 31 aid in stabilizing such .palletas it is moved along the tracks provided for it. The chain itself isgenerally indicated at 32 in FIGS. 1 and 3.

Turning now to FIG. 3, a series of work stations is illustrated ascomprised of the mechanisms generally indicated at 33a, 33b and 33c.These work stations are only diagrammatically illustrated in that theymay take any of a great variety of forms. An object of the'invention isto divert the pallet 10 from the main track Ila, 1 1b to these workstations successively by reason of the side tracks 12a, 12b and theconstructions heretofore detailed. As illustrated in connection with thework station 33a, there is a side track 12a, 12b which brings the pallet10 into proper position with respect to this station. A side conveyorchain 34, which is like the segmented chain 32 and which runs at thesame speed,

furnishes the motive power for moving the pallet 10 along the side track12a, 12!: when it is cantilevered thereto as herein before described. Asmentioned before, and as shown at 12c and 12d, portions of the sidetrack 12a, 12!; are parallel to portions of the main track 11a, 11b. Thechains 32 and 34 also parallel one another in these regions. Just as therail 12a is at the same level as the rail 11a, so is the chain 34 at thesame level as the chain 32. The plate 31 is of such width that itextends outwardly beyond the chain 32. Thus, when the pallet is movedinto the region at which the track portion 12c is parallel to the rail11a and at which time the chain 34 is parallel to, and adjacent to, thechain 32, such plate 31 will engage the chain 34 while it is stillengaged with the chain 32. It will be apparent, therefore, that for arelatively brief period not only is the pallet supported from the maintrack 11a, 11b and side track 12a, 12b (in the vicinity, for example, ofthe side track portion 12c) but also such pallet 10 is driven by both ofthe chains 32 and 34. It is at this point that the bar 24 is actuated soas to move the combined arm 19a and cam plate 21 from the position ofFIG. 4 to that of FIG. 5 whereby to disengage the pallet 10 fromcantilevered support on the main track 11a, 1 lb and to effect a similarcantilevered engagement of the pallet 10 on the side track 12a, 12b. Itwill be apparent, therefore,

that continued movement of the chains 32 and 34 will result in thepallet 10 moving along the side track 12a, 12b to the work station, forexample, 33a. Appropriate mechanism, not shown, will be employed to stopthe pallet in proper position beneath the working mechanism at thestation 330. Such means are conventional in conveyor systems.

It will be understood that the arrangement just described in connectionwith the work station 33a will be repeated for each of the work stations33b and 33c and for any others that may be included in the system.

As best seen in FIGS. 1 and 2 the main track rails 11a and 11b and theside track rails 12a and 12b may be supported by any convenientstructure such as is generally indicated at 35 and 36. Additionally ithas been found useful to provide mechanism, particularly in connectionwith the structure 36 and the various work stations 33a, 33b and 330,for lifting the friction plate 31 from contact with the side conveyor 34when the pallet has been stopped, so as to cut down wear on ,thefriction material provided for this plate. Such mechanism may include anair cylinder 37, a pair of rods 38 and 39 pivoted to appropriate framestructure as indicated at 40 and a pivoted connection of the rod 39 tothe plate 31 as indicated at 41. The cylinder 37 will also be pivoted toappropriate frame structure as indicated at 42. The upper ends of thearms 39 have pins 43 extending therefrom to a position beneath the plate31. When the pallet 10 is stopped in position beneath a work stationsuch as indicated at 33a by conventional means as earlier indicated, theair cylinder 37 will be actuated in a known manner whereby to move thearm 39 so as to life the plate 31 from the chain it heretofore engaged.

The parts conveyor pallet 10 and related mechanism may include otherfeatures of benefit in conveyor systems. When, for example, it isdesired to switch the pallet 10 from the main track to a selected sidetrack, this may be accomplished by providing the pallet with a series ofactuating pins 44a, b, c and d located at different heights, one foreach work station, which pins will engage appropriate hammer mechanism,at such time as the pallet 10 is riding on both the main track and aside track, whereby the plunger 29 will be actuated to strike the bar 24and shift it, for example, from the position of FIG. 4 to that of FIG. 5whereby to effect transfer of the pallet 10 from cantilevered engagementon the main track to similar cantilevered engagement on the side track.The details of this mechanism are not shown. I

Considering the pallet and conveyor mechanism generally, although notshown in detail, it will be understood that the pins 44a, b, c and d,located at different heights, are designed to actuate switch mechanismsaccording to the particular work station that the pallet is to be guidednext. The pin and its respective mechanism will actuate the air operatedplunger 29 previously mentioned whereby to at that point effect transferof the pallet 10 from its cantilevered position on the main track 11a,11b to similar cantilevered position on the particular side track 12a,12b selected as determined by position of the involved pin 44. Otherconventional mechanism will stop movement of the pallet 10 and lock itin place under the particular work station 33 selected. The air cylinder37 and related mechanisms, although shown in FIG. 1 as positioned underthe main track chain 32, will normally be associated with the side trackchain 34 so that when the pallet 10 is locked beneath a work station 33,actuation of the air cylinder 37 will cause the friction plate 31 to beurged against its spring means and out of drag contact with the flatsegmented (crescent) chain 34 so as to prevent wear on this plate. Whenthe pallet is unlocked and the plate 31 again brought into contact withthe chain 34, the pallet will move along the side track until itreaches, for example, side track portion 12d which is parallel to themain track 11a. Mechanisms similar to those previously described willactuate another air operated plunger 29 whereby to actuate the bar 24and move it from the right-hand position shown in FIG. 5 to theleft-hand position shown in FIG. 4 so that the pallet will again besupported in cantilever fashion from the main track 11a, 11b. The springloaded friction plate 31 which extends beyond the side track chain 34will at this time be in engagement with the main track chain 32 wherebythe pallet will now continue its movement on the main track untilshunted to another side track for performance of another operation byanother work station, such further transfer of the pallet from the maintrack to a side track to be accomplished as described in connection withthe station 33a.

It will be apparent to those skilled in the art that modifications maybe made in this invention without departing from the scope and spiritthereof. Although the invention has been described in terms ofparticular structures, mechanisms and arrangements, this has been donefor exemplary purposes only and the invention is not to be limited tothese unless they are specifically set forth in the subjoined claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A pallet adapted to be supported in cantilever fashion from a maintrack comprised of a first pair of parallel, vertically alignedelongated members, said pallet comprising a' body, at least one firstupper roller journaled in said body at one side thereof, at least onefirst lower roller journaled in said body at said one side, and a firstclamping roller mounted in said body for selective movement towards andaway from one of said first upper and said first lower rollers, wherebywhen said first upper roller is engaged on one of said elongated membersand said first lower rolleris engaged on the other of said elongatedmembers, movement of said first clamping roller into engagement with oneof said first pair of elongated members will result in said pallet beingcantilevered from said main track; said pallet being adapted to besupported in cantilever fashion from either said main track or from aside track comprised of a second pair of parallel, vertically alignedelongated members having portions thereof spaced from and parallel to,in respective horizontal planes, said said first pair of elongatedmembers; said pallet having at least one second upper roller journaledin said body at the side opposite said one side, at least one secondlower roller journaled in said body at said opposite side, and a secondclamping roller mounted in said body for selective movement towards andaway from one of said second upper and lower rollers, whereby when saidsecond upper roller is engaged on one of said second elongated membersand said second lower roller is engaged on the other of said secondelongated members, movement of said second clamping roller intoengagement with one of said second elongated members will result in saidpallet being cantilevered from said side track when said first clampingroller is disenggaged from said one of said first pair of elongatedmembers.

2. The pallet of claim 1 in which there are a pair of said first upperrollers and a pair of said second upper rollers, a pair of said firstlower rollers and a pair of said second lower rollers, a pair of saidfirst clamping rollers and a pair of second clamping rollers, said pairof first clamping rollers being movable towards and away from said pairof first upper rollers and said pair of second clamping rollers beingmovable towards and away from said pair of second upper rollers.

3. A pallet-conveyor system including a main track comprised of a firstpair of parallel, vertically aligned elongated members; a side trackcomprised of a second pair of parallel, vertically aligned elongatedmembers having portions which are spaced from and'parallel tocorresponding portions of said first mentioned elongated members; apallet having a pair of first upper rollers adapted to engage the upperof said main track elongated members and a pair of second upper rollersadapted to engage the upper of said side track elongated members; saidpallet having a pair of first lower rollers adapted to engage the lowerof said main track elongated members and a pair of second lower rollersadapted to engage the lower of said side track elongated members; saidpallet having a shaft rotatably mounted therein, a pair of arms fixed tosaid shaft for rotation therewith, a first pair of clamping rollers,each of said arms having one such first clamping roller journaled on oneend thereof opposite one another, a second pair of clamping rollers,each of said arms having one such second clamping roller journaled onthe other end thereof opposite one another, and means to rock said shaftand said arms so as alternatively to engage said first pair of clampingrollers with said upper of said main track elongated members and saidsecond pair of clamping rollers with said upper of said side trackelongated members, whereby said pallet is cantilevered either from saidmain track or from said side track.

4. The system of claim 3 including a first drive chain for said maintrack and a second drive chain for said side track, said first and saidsecond drive chains running at the same speed, said drive chains beingclosely adjacent one another in the region wherein the said portions ofsaid main track and said side track are parallel to one another, andsaid pallet having a spring biased friction plate normally engaging saidfirst drive chain and being adapted to engage said second drive chainwhen said drive chains are closely adjacent one another.

5. The system of claim 4 including a work station serviced by said sidetrack, means to stop said pallet at said work station, and means todisengage said friction plate from said second chain when said pallet isso stopped.

6. The system of claim 3 in which said means to rock said shaftcomprises cam means associated with said shaft, shiftable means toengage said cam means, and means to actuate said shiftable means whensaid pallet is supported on said spaced, parallel portions of said firstand said second pairs of elongated members, whereby to alternatelychange cantilevered support of said pallet from said main track to saidside track and vice versa.

1. A pallet adapted to be supported in cantilever fashion from a maintrack comprised of a first pair of parallel, vertically alignedelongated members, said pallet comprising a body, at least one firstupper roller journaled in said body at one side thereof, at least onefirst lower roller journaled in said body at said one side, and a firstclamping roller mounted in said body for selective movement towards andaway from one of said first upper and said first lower rollers, wherebywhen said first upper roller is engaged on one of said elongated membersand said first lower roller is engaged on the other of said elongatedmembers, movement of said first clamping roller into engagement with oneof said first pair of elongated members will result in said pallet beingcantilevered from said main track; said pallet being adapted to besupported in cantilever fashion from either said main track or from aside track comprised of a second pair of parallel, vertically alignedelongated members having portions thereof spaced from and parallel to,in respective horizontal planes, said said first pair of elongatedmembers; said pallet having at leaSt one second upper roller journaledin said body at the side opposite said one side, at least one secondlower roller journaled in said body at said opposite side, and a secondclamping roller mounted in said body for selective movement towards andaway from one of said second upper and lower rollers, whereby when saidsecond upper roller is engaged on one of said second elongated membersand said second lower roller is engaged on the other of said secondelongated members, movement of said second clamping roller intoengagement with one of said second elongated members will result in saidpallet being cantilevered from said side track when said first clampingroller is disenggaged from said one of said first pair of elongatedmembers.
 1. A pallet adapted to be supported in cantilever fashion froma main track comprised of a first pair of parallel, vertically alignedelongated members, said pallet comprising a body, at least one firstupper roller journaled in said body at one side thereof, at least onefirst lower roller journaled in said body at said one side, and a firstclamping roller mounted in said body for selective movement towards andaway from one of said first upper and said first lower rollers, wherebywhen said first upper roller is engaged on one of said elongated membersand said first lower roller is engaged on the other of said elongatedmembers, movement of said first clamping roller into engagement with oneof said first pair of elongated members will result in said pallet beingcantilevered from said main track; said pallet being adapted to besupported in cantilever fashion from either said main track or from aside track comprised of a second pair of parallel, vertically alignedelongated members having portions thereof spaced from and parallel to,in respective horizontal planes, said said first pair of elongatedmembers; said pallet having at leaSt one second upper roller journaledin said body at the side opposite said one side, at least one secondlower roller journaled in said body at said opposite side, and a secondclamping roller mounted in said body for selective movement towards andaway from one of said second upper and lower rollers, whereby when saidsecond upper roller is engaged on one of said second elongated membersand said second lower roller is engaged on the other of said secondelongated members, movement of said second clamping roller intoengagement with one of said second elongated members will result in saidpallet being cantilevered from said side track when said first clampingroller is disenggaged from said one of said first pair of elongatedmembers.
 2. The pallet of claim 1 in which there are a pair of saidfirst upper rollers and a pair of said second upper rollers, a pair ofsaid first lower rollers and a pair of said second lower rollers, a pairof said first clamping rollers and a pair of second clamping rollers,said pair of first clamping rollers being movable towards and away fromsaid pair of first upper rollers and said pair of second clampingrollers being movable towards and away from said pair of second upperrollers.
 3. A pallet-conveyor system including a main track comprised ofa first pair of parallel, vertically aligned elongated members; a sidetrack comprised of a second pair of parallel, vertically alignedelongated members having portions which are spaced from and parallel tocorresponding portions of said first mentioned elongated members; apallet having a pair of first upper rollers adapted to engage the upperof said main track elongated members and a pair of second upper rollersadapted to engage the upper of said side track elongated members; saidpallet having a pair of first lower rollers adapted to engage the lowerof said main track elongated members and a pair of second lower rollersadapted to engage the lower of said side track elongated members; saidpallet having a shaft rotatably mounted therein, a pair of arms fixed tosaid shaft for rotation therewith, a first pair of clamping rollers,each of said arms having one such first clamping roller journaled on oneend thereof opposite one another, a second pair of clamping rollers,each of said arms having one such second clamping roller journaled onthe other end thereof opposite one another, and means to rock said shaftand said arms so as alternatively to engage said first pair of clampingrollers with said upper of said main track elongated members and saidsecond pair of clamping rollers with said upper of said side trackelongated members, whereby said pallet is cantilevered either from saidmain track or from said side track.
 4. The system of claim 3 including afirst drive chain for said main track and a second drive chain for saidside track, said first and said second drive chains running at the samespeed, said drive chains being closely adjacent one another in theregion wherein the said portions of said main track and said side trackare parallel to one another, and said pallet having a spring biasedfriction plate normally engaging said first drive chain and beingadapted to engage said second drive chain when said drive chains areclosely adjacent one another.
 5. The system of claim 4 including a workstation serviced by said side track, means to stop said pallet at saidwork station, and means to disengage said friction plate from saidsecond chain when said pallet is so stopped.